Magnetic resonance is a known technology for, inter alia, obtaining images of the interior of an item being examined. In a magnetic resonance device a static basic magnetic field generated by a basic field magnet is overlaid with gradient fields switched at high speed and generated by a gradient coil system. The magnetic resonance device further includes a radio frequency (RF) antenna which radiates radio frequency signals into the item being examined in order to trigger magnetic resonance signals, and registers the triggered magnetic resonance signals on the basis of which magnetic resonance images are produced.
A magnetic resonance device is known from DE 44 14 371 A1 in which a radio frequency shield is located between a radio frequency antenna and a gradient coil system of the magnetic resonance device and is embodied in such a way as to be permeable in the low-frequency range for the electromagnetic fields generated by the gradient coil system and impermeable in the radio frequency range for the fields generated by the radio frequency antenna. The radio frequency shield contains a first electrically conducting layer arrangement and a second such arrangement located opposite the first, mutually separated by a dielectric, with said layer arrangements containing strip conductors arranged side-by-side and mutually separated by electrically insulating slots, with the slots in the first layer arrangement being displaced relative to those in the second arrangement, and with adjacent strip conductors being interconnected in at least one layer arrangement via specifically arranged jumpers which conduct radio frequency currents and which contain, for example, capacitors.
Possible embodiments of a radio frequency shield are known from, for instance, DE 34 45 724 A1, wherein, for example, shielding layers are arranged on both sides of the gradient coil system of the magnetic resonance device.
The radio frequency antenna of the magnetic resonance device is embodied in the form of, for example, what is termed a birdcage antenna. A birdcage antenna for generating a homogeneous radio frequency field within a volume enclosed thereby is generally embodied in such a way that conductors are arranged mutually parallel and equidistantly spaced on a cylinder jacket and are interconnected by means of end rings. Tuning to the high-pass and low-pass filter ranges is therein effected by introducing capacitances in each of the conductors or the end rings between the conductors so that a homogeneous radio frequency field results in the event of resonance. Embodiments of a birdcage antenna of said type can be found in, for example, U.S. Pat. No. 4,680,548.